Teleflex Speedometer displayed speed not accurate

[Augoose]

This is on a 1989 20' bow rider with Mercruiser Alpha 1 Lower unit.

What would cause a speedometer to operate but not display the accurate speed? In other words, my speedometer won't register anything until I'm going about 15-18 mph at which point it reads about 10 mph. Then at about 25-30 mph it reads 15-20 mph. I inspected the pitot and tube and it doesn't seem to be blocked or collapsed. I disconnected the speedo end of the tube and blew air through the line which resulted in bubbles coming out of the pitot so I know its not completely blocked. I've verified actual speed with a GPS.

Could the pitot be bad or is it likely the speedometer gauge itself? I would have thought that when the gauge goes, it would go completely?

Thanks!

 

[j_martin]

Re: Teleflex Speedometer displayed speed not accurate

Common knowledge, any pitot speedometer's reading is a scientific wild a**ed guess. You could enlarge the pitot a bit at a time till the guess gets closer.

 

[Augoose]

Re: Teleflex Speedometer displayed speed not accurate

I was thinking about doing that, however I'm hesitant to modify anything until I rule out component failure because at some point it must have worked as the engineers designed it, right?:facepalm:
What do I have to lose though.....a $4.00 pitot? Where's my drill bit.....